Nozzle flapper mechanism

ABSTRACT

A nozzle flapper mechanism includes an electrostrictive device, a plate member coupled to the electrostrictive device, a nozzle having an orifice facing the electrostrictive device or the plate member, and a controller for applying a voltage to the electrostrictive device to keep a nozzle back pressure constant or vary the nozzle back pressure. The electrostrictive device comprises a shim, piezoelectric ceramics members disposed on the shim, and thin-film electrodes disposed on the piezoelectric ceramics members, the electrodes having an area smaller than that of the piezoelectric ceramics members, the piezoelectric ceramics members having one end directly fixed in position on a stationary member.

This application is a division of application Ser. No. 301,708, filedJan. 26, 1939, now U.S. Pat. No. 4,934,401 issued Jun. 19, 1990.

BACKGROUND OF THE INVENTION

The present invention relates to a nozzle flapper mechanism, and moreparticularly to a nozzle flapper mechanism for use in anelectropneumatic transducer for converting an electric signal to a fluidpressure signal, especially a pneumatic pressure signal, the nozzleflapper mechanism having, as a transducer element, a nozzle flapperbeing in the form of a bimorph electrostrictive (piezoelectric) device,and being capable of converting a low-voltage electric signal accuratelyto a pneumatic pressure signal.

Heretofore, torque motors have widely been used as a device forconverting an electric signal to a pneumatic pressure signal. Anelectric current is supplied to the coil of the torque motor to producea corresponding rotational movement which is converted to an amount ofdisplacement for conversion into a pneumatic pressure signal through anozzle flapper, a pilot valve, or the like. Where a control device suchas an electropneumatic transducer is constructed of such a torque motor,the greater the torque produced by the torque motor, the higher theresistance the control device has against mechanical vibrations ordisturbances and the more stable the control device is.

In view of the recent trend toward smaller and lighter control devices,it is very important to construct the torque motor in a small size.However, the smaller the torque motor, the lower the torque that can begenerated by the torque motor dependent on the value of the electriccurrent supplied thereto. As a result, the control device would besusceptible to mechanical vibrations or other disturbances, and it wouldbe technically impossible to employ any torque motor in certainapplications in which the control device is supposed to be used.

The inventor filed U.S. patent application Ser. No. 729,188 for anelectropneumatic transducer unit which employs an electrostrictivedevice for converting an electric signal to a pneumatic pressure signal.

According to the invention of the above U.S. patent application, theelectrostrictive device is of the bimorph type in the form of a thinrectangular shape having one end fixed and the other as a free end. Whena voltage is applied to electrodes with the electrostrictive devicefixed at one end, the free end thereof is slightly displaced. Therefore,where the electrostrictive device is constructed as a nozzle flapper, itcan convert a variation in the applied voltage easily to a nozzle backpressure, i.e., a pneumatic pressure signal.

The electrostrictive device as a nozzle flapper may be fixed in positionas follows: As shown in FIGS. 1 through 3 of the accompanying drawings,a nozzle flapper mechanism 2 includes a base 4 on which a firstcolumn-shaped fixing plate 6a is disposed. An electrostrictive device 8is placed on the first fixing plate 6a. One end of the electrostrictivedevice 8 is fastened to the first fixing plate 6a by a secondcolumn-shaped fixing plate 6b which is coupled to the first fixing plate6b by means of a pair of fastening screws 10 threaded into threadedholes in the first fixing plate 6a. A nozzle 12 is fixedly mounted onthe base 4 and has a distal upper end positioned closely to theelectrostrictive device 8. The other end of the electrostrictive device8 remote from the first and second fixing plates 6a , 6b is not limitedin motion, but serves as a free end.

The first and second fixing plates 6a, 6b may be made of an electricallyinsulative material or an electrically conductive material. Where theyare made of an electrically conductive material, it is necessary toplace insulating sheets on them in contact with electrodes of theelectrostrictive device 8. An auxiliary plate 14 made of ceramics or thelike is attached to the free end of the electrostrictive device 8 forpreventing the electrostrictive device 8 from being damaged by thenozzle 12 when the electrostrictive device 8 is flexed when a voltage isapplied thereto.

The electrostrictive device 8 is of the construction shown in FIG. 1. Arectangular shim 16 made of an electrically conductive material such asphosphor bronze stainless steel, or the like. Piezoelectric ceramicsmembers 18a, 18b are bonded to upper and lower surfaces, respectively,of the shim 16 by an adhesive. Thin-film electrodes 19a, 19b are placedon upper and lower surfaces, respectively, of the piezoelectric ceramicsmembers 18a, 18b. The piezoelectric ceramics members 18a, 18b cover mostof the surface areas of the shim 16. When the electrostrictive device 8is fixedly positioned by the fastening screws 10, the electrostrictivedevice 8 which is composed of the electrode 19a, the piezoelectricceramics member 18a, the shim 16, the piezoelectric ceramics member 18b,and the electrode 19b, arranged in the order named in the upwarddirection, is firmly gripped between the first and second fixing plates6a, 6b .

In operation, a DC voltage is applied to the electrostrictive device 8.Since the piezoelectric ceramics member 18b tends to extend and thepiezoelectric ceramics member 18a tends to shrink, the free end of theelectrostrictive device 8 is flexed largely toward the nozzle 12 andapproaches the orifice of the nozzle 12. Since the amount of flexingdisplacement of the electrostrictive device 8 is proportional to theapplied voltage, the nozzle flapper mechanism can produce a fluidpressure signal dependent on the applied voltage signal.

Generally, it is known that when a voltage is impressed on theelectrostrictive device 8, the applied voltage and the amount ofdisplacement of the free end of the electrostrictive device 8 arerelated to each other as shown in FIG. 4. As the applied voltage isgradually increased from 0, the electrostrictive device 8 is deformedalong a curve from a to b in FIG. 4. When the applied voltage isthereafter lowered, the displacement curve goes from b to c, but notfrom b to a. When the voltage is applied again, the electrostrictivedevice 8 is deformed along another curve from c to b.

Stated otherwise, when the applied voltage is lowered and then increasedagain, the deformation of the electrostrictive device 8 undergoeshysteresis. This phenomenon of hysteresis particularly manifests itselfwith the bimorph electrostrictive device. Even if the same voltage isapplied, the displacement of the free end of the electrostrictive device8 is varied with time as indicated by a shift from the curve from b to cto a curve from b' to c'.

When a constant voltage remains applied to the electrostrictive device 8for a certain period of time, the displacement of the free end of theelectrostrictive device 8 is increased with time as represented by thesolid-line curve in FIG. 5, the phenomenon being referred to as creepingof the electrostrictive device. The creeping is understood as dependingupon the material of the piezoelectric ceramics, the thickness andmaterial of the shim, the adhesive used, the manner in which theelectrostrictive device is fixed, and other parameters. The inventor hasmade various attempts to avoid the creeping, and found that adisplacement caused by the creeping ranges from 10% to several tens %.The creeping is liable to be promoted when the ambient temperaturevaries.

The creeping is caused largely by the characteristics which theelectrostrictive device itself has. On the other hand, it has beenconfirmed that the creeping is also developed by the fact that thepiezoelectric ceramics members 18a, 18b are fixed to the shim 16 by theadhesive, and that the first and second fixing plates 6a, 6b are curvedat their opposite ends by the strongly tightened fastening screws 10which are threaded into the base 4 through relatively large holesdefined in the fixing plates 6a, 6b, thus pressing the corners of theelectrostrictive device 8 as shown in FIG. 6. When a relatively lowvoltage, say about 10V, is applied to the electrostrictive device 8 forfine controlling action, any displacement caused on the electrostrictivedevice 8 is very small, resulting in the need for controlling movementsfor a distance on the order of a few microns. Accordingly, the forceswith which the fastening screws 10 are to be tightened have to beadjusted very carefully.

However, it is virtually impossible to tighten the two fastening screws10 with equal forces, and the electrostrictive device 8 is usuallysubjected to irregular stresses due to uneven screw tightening forcesapplied.

Furthermore, the portions of the piezoelectric ceramics members whichare gripped by the fixing plates are also expanded and contracted by theapplication of a voltage thereto. Internal stresses developed in thepiezoelectric ceramics members are therefore varied, causing thecreeping which will make it difficult to effect accurate control. Morespecifically, upon application of a DC voltage to the electrostrictivedevice, the portions of the piezoelectric ceramics members which areheld against the electrodes are expanded and contracted. With thepiezoelectric ceramics members being tightened by the fixing plates, theabove expansion and contraction cause stresses to be varied slightly inthe tightened portions of the piezoelectric ceramics members. It hasbeen confirmed that the electrostrictive device is expanded andcontracted in a direction normal to the direction of forces with whichit is tightened by the fixing plates, thereby producing local "slippage"of the electrostrictive device with respect to the fixing plates. Suchslippage is also greatly responsible for the creeping.

The use of an electrostrictive device for the conversion of an electricsignal to a pneumatic pressure signal is to achieve a desired signalconversion capability through accurate and fine electric control. Wherethe creeping as described above exists, however, even if a controlvoltage applied to the electrostrictive device is kept at a constantlevel to develop a fixed nozzle back pressure, the nozzle back pressuretends to be varied by the creeping. It would be essentially difficult toeffect accurate control of a valve body or the like using a nozzle backpressure if the displacement of an electrostrictive device based on thecreeping reached several tens %.

SUMMARY OF THE INVENTION

In view of the aforesaid drawbacks of the conventional nozzle flappermechanisms, it is an object of the present invention to provide a nozzleflapper mechanism including piezoelectric ceramics members andelectrodes, at least the piezoelectric ceramics members or theelectrodes being either not gripped between fixing plates, or grippedbetween the fixing plates at as small a region as possible, or thepiezoelectric ceramics members being directly held by a holder, so thatthe nozzle flapper mechanism is not affected by tightening forcesapplied by fastening screws and is capable of easily and accuratelyconverting an electric signal to a pneumatic pressure signal.

Another object of the present invention is to provide a nozzle flappermechanism comprising: an electrostrictive device; a plate member coupledto said electrostrictive device; a nozzle having an orifice facing saidelectrostrictive device or said plate member; and means for applying avoltage to said electrostrictive device to keep a nozzle back pressureconstant or vary the nozzle back pressure; said electrostrictive devicecomprising a shim, a piezoelectric ceramics member disposed on saidshim, and a thin-film electrode disposed on said piezoelectric ceramicsmember, said electrode having an area smaller than that of saidpiezoelectric ceramics member, said piezoelectric ceramics member havingone end directly fixed in position.

Still another object of the present invention is to provide a nozzleflapper mechanism further including a fixing plate by which said one endof the piezoelectric ceramics member is fixed in position.

Yet another object of the present invention is to provide a nozzleflapper mechanism wherein said electrode has a narrow lead extendingrespectively therefrom and terminating short of an end of saidpiezoelectric ceramics member.

Yet another object of the present invention is to provide a nozzleflapper mechanism wherein said lead terminates at a longitudinal centralportion of said piezoelectric ceramics member.

Yet still another object of the present invention is to provide a nozzleflapper mechanism wherein said lead terminates at a longitudinal endcorner of said piezoelectric ceramics member.

A further object of the present invention is to provide a nozzle flappermechanism wherein said fixing plate has a slot defined therein andreceiving said lead.

A still further object of the present invention is to provide a nozzleflapper mechanism wherein said piezoelectric ceramics member has a slotdefined therein and extending to the end thereof, said lead beingreceived in said slot of the piezoelectric ceramics member.

A yet still further object of the present invention is to provide anozzle flapper mechanism further including a spacer disposed betweensaid piezoelectric ceramics plate and said fixing plate.

It is also an object of the present invention to provide a nozzleflapper mechanism comprising: an electrostrictive device; a plate membercoupled to said electrostrictive device; a nozzle having an orificefacing said electrostrictive device or said plate member; and means forapplying a voltage to said electrostrictive device to keep a nozzle backpressure constant or vary the nozzle back pressure; saidelectrostrictive device comprising a plurality of piezoelectric ceramicsmembers, and a plurality of thin-film electrodes disposed on faces andbacks of said piezoelectric ceramics members.

Yet another object of the present invention is to provide a nozzleflapper mechanism further including an electric conductor connected toalternating ones of said electrodes on said piezoelectric ceramicsmembers and connecting said alternating ones of the electrodes to apower supply.

Yet another object of the present invention is to provide a nozzleflapper mechanism wherein said electrodes have leads extendingrespectively therefrom, the lead from each of said electrodes beingpositioned on an opposite side to the lead from an adjacent one of saidelectrodes.

Still another object of the present invention is to provide a nozzleflapper mechanism wherein the leads from said electrodes are positionedalternately on opposite sides.

Yet another object of the present invention is to provide a nozzleflapper mechanism comprising: an electrostrictive device; a plate membercoupled to said electrostrictive device; a nozzle having an orificefacing said electrostrictive device or said plate member; and means forapplying a voltage to said electrostrictive device to keep a nozzle backpressure constant or vary the nozzle back pressure; saidelectrostrictive device comprising a shim, a piezoelectric ceramicsmember disposed on said shim, and a thin-film electrode disposed on saidpiezoelectric ceramics member, said electrode having an area smallerthan that of said piezoelectric ceramics member, said piezoelectricceramics member having one end fixed to a holder directly by solderingor adhesive bonding.

Yet still another object of the present invention is to provide a nozzleflapper mechanism a nozzle flapper mechanism comprising: anelectrostrictive device; a plate member coupled to said electrostrictivedevice; a nozzle having an orifice facing said electrostrictive deviceor said plate member; means for applying a voltage to saidelectrostrictive device to keep a nozzle back pressure constant or varythe nozzle back pressure; said electrostrictive device comprising ashim, a piezoelectric ceramics member disposed on said shim, and athin-film electrode disposed on said piezoelectric ceramics member; andmeans for gripping said shim only.

A further object of the present invention is to provide a nozzle flappermechanism wherein said shim is substantially T-shaped.

A still further object of the present invention is to provide a nozzleflapper mechanism wherein said shim includes a region free from saidpiezoelectric ceramics member and said electrode, said region having aplurality of holes spaced from each other, said shim being fixed inposition by screws extending through said holes, respectively.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

cl BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a nozzle flapper mechanismincluding a conventional bimorph electrostrictive device;

FIG. 2 is a plan view of the nozzle flapper mechanism shown in FIG. 1;

FIG. 3 is a front elevational view of the nozzle flapper mechanism ofFIG. 1;

FIG. 4 is a graph showing the relationship between a voltage applied tothe conventional bimorph electrostrictive device and an amount ofdisplacement thereof;

FIG. 5 is a graph showing creeping developed when a voltage remainsapplied to the conventional bimorph electrostrictive device for a longperiod of time;

FIG. 6 is a front elevational view showing how the nozzle flappermechanism of FIG. 1 is flexed;

FIG. 7 is a perspective view of an electrostrictive device to beincorporated in a nozzle flapper mechanism according to the presentinvention;

FIG. 8 is a plan view of the electrostrictive device shown in FIG. 7;

FIG. 9 is a cross-sectional view taken along line IX--IX of FIG. 8;

FIG. 10 is a cross-sectional view taken along line X--X of FIG. 8;

FIG. 11 is a front elevational view of the electrostrictive device shownin FIG. 7;

FIG. 12 is a schematic view showing an electropneumatic transducer inwhich the electrostrictive device of the invention is incorporated;

FIG. 13 is a schematic view of a positioner incorporating theelectropneumatic transducer shown in FIG. 12;

FIG. 14 is a perspective view of an electrostrictive device according toanother embodiment of the present invention;

FIG. 15 is a plan view of an electrostrictive device according to stillanother embodiment of the present invention;

FIG. 16 is a vertical cross-sectional view, partly cut omitted fromillustration, of the electrostrictive device illustrated in FIG. 15;

FIG. 17 is an exploded perspective view of the electrostrictive deviceof the invention and fixing plates for fixing the electrostrictivedevice;

FIG. 18 is a perspective view of an electrostrictive device according toyet another embodiment of the present invention;

FIG. 19 is a vertical cross-sectional view of the electrostrictivedevice of FIG. 18;

FIG. 20 is an exploded perspective view of the electrostrictive deviceof the invention and fixing plates of another embodiment for fixing theelectrostrictive device;

FIG. 21 is a perspective view of an electrostrictive device inaccordance with a further embodiment of the present invention;

FIG. 22 is a perspective view of an electrostrictive device inaccordance with a still further embodiment of the present invention;

FIG. 23 is a perspective view of an electrostrictive device inaccordance with a yet further embodiment of the present invention;

FIG. 24 is a perspective view of a nozzle flapper mechanism according toanother embodiment of the present invention, showing a laminatedstructure of piezoelectric ceramics members and electrodes;

FIG. 25 is a cross-sectional view taken along line XXV--XXV of FIG. 24;

FIG. 26 is a perspective view of a nozzle flapper mechanism according tostill another embodiment of the present invention, showing a laminatedstructure of piezoelectric ceramics members and electrodes;

FIG. 27 is a view as viewed in the direction of the arrow D in FIG. 26;and

FIG. 28 is a view as viewed in the direction of the arrow E in FIG. 26.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is particularly applied to the configuration of anelectrostrictive device.

According to a first embodiment shown in FIG. 7, an electrostrictivedevice 30 includes a shim 32 having a rectangular shape. The shim 32 ismade generally of a metallic material such as phosphor bronze, stainlesssteel, or the like. Two piezoelectric ceramics members 34a, 34b arebonded to the opposite surfaces, respectively, of the shim 32 with anadhesive therebetween. The shim 32 has one end slightly projectingoutwardly from the corresponding ends of the piezoelectric ceramicsmembers 34a, 34b.

Two thin-film electrodes 36a, 36b are attached to the outer exposedsurfaces, respectively, of the piezoelectric ceramics members 34a, 34b.As illustrated in FIG. 7, the electrodes 36a, 36b are substantiallyrectangular in shape and have a width or transverse dimension which issubstantially the same as the width of the piezoelectric ceramicsmembers 34a, 34b. Very narrow leads 38a, 38b extend respectively fromthe transverse centers of the electrodes 34a, 34b and terminate at theends of the piezoelectric ceramics members 34a, 34b (see FIGS. 7, 8, and10). An auxiliary plate 14 is attached to the lower surface of the freeend of the electrostrictive device 30.

As shown in FIGS. 7 through 10, the electrostrictive device 30 isincorporated in a nozzle flapper mechanism in which the leads 38a, 38bof the electrodes 36a, 36b are placed over a first fixing plate 6a, anda second fixing plate 6b is positioned on the electrostrictive device30. The electrostrictive device 30 is then firmly gripped between thefirst and second fixing devices 6a, 6b by means of fastening screws 10extending through holes defined in the first and second fixing plates 10and threaded into a base 4. The region of the electrostrictive device 30which is clamped by the fastening screws 10 is free of the electrodes36a, 36b, but only includes the leads 38a, 38b which are about 1 mm wideand a few μm thick. Therefore, only the shim 32, the piezoelectricceramics members 34a , 34b , and the leads 38a, 38b are subjected totightening forces with which the electrostrictive device 30 is fastenedby the fastening screws 10. It is therefore not necessary to adjust suchtightening forces with great care when fixing the electrostrictivedevice 30 to the fixing plates 6a, 6b.

When a voltage is applied to the electrostrictive device 30 that iscombined with an electropneumatic transducer to convert an electricsignal to a pneumatic pressure signal, any creeping of theelectrostrictive device 30 is greatly reduced and hence theelectrostrictive device 30 operates accurately and stably. It ispossible to effect precise control especially when the electrostrictivedevice 30 is driven by a low voltage.

The electropneumatic transducer in which the electrostrictive device 30of the invention is incorporated will be described below.

As illustrated in FIG. 12, the electrodes 36a, 36b attached to thepiezoelectric ceramics members 34a , 34b are electrically connected toeach other and also to one terminal of a controller 50. The otherterminal of the controller 50 is electrically coupled to the shim 32. Anozzle 12 placed on the base 4 is pneumatically connected to a pilotvalve 52 which has an output port branched and connected to apneumatic-to-electric signal transducer 54, the output terminal of whichis connected to the controller 50. The controller 50 is supplied with acontrol signal S.

When the control signal S is applied to the controller 50, thecontroller 50 applies a predetermined voltage between the electrodes36a, 36b on the piezoelectric ceramics members 34a , 34b and the shim 32to cause the free end of the electrostrictive device 30 to be flexed inproportion to the voltage. As a result, the nozzle back pressure of airejected from the nozzle 12 is varied, and such a pressure variation isintroduced into the pilot valve 52. An output signal from the pilotvalve 52 is applied to a certain device to control the device.

The output signal from the pilot valve 52 is also applied to thepneumatic-to-electric signal transducer 54 which applies it as afeedback signal to the controller 50.

FIG. 13 shows a positioner incorporating the electropneumatic transducerdescribed above.

Those parts in FIG. 13 which are identical to those of theelectropneumatic transducer are denoted by identical reference numerals,and will not be described in detail.

In FIG. 13, the output signal from the pilot valve 52 is applied to acontrol valve 60 to control the control valve 60, and an output signalfrom the control valve 60 is branched and applied to a sensor 62 forconverting a displacement of the control valve 60 to a correspondingelectric signal. The sensor may preferably be a potentiometer. An outputsignal from the potentiometer 62 is applied as a feedback signal to thecontroller 50. Therefore, the output signal applied to the pilot valve52 displaces the control valve 60, and the output signal from the sensor62 which is proportional to the displacement of the control valve 60 isapplied to the controller 50 for feedback control.

FIG. 14 shows an electrostrictive device 30 according to anotherembodiment of the present invention. The electrostrictive device 30 ofFIG. 14 includes electrodes 36a, 36b having respective leads 38a, 38bwhich are positionally displaced to one side of piezoelectric ceramicsmembers 34a , 34b with respect to longitudinal central lines thereof.Therefore, lead wires connected to a shim 32 and the electrodes 36a, 36bmay be gathered and connected to one end corner thereof so that theselead wires will not physically interfere with other accessories anddevices disposed near the electrostrictive device 30.

FIGS. 15 and 16 illustrate an electrostrictive device according to stillanother embodiment of the present invention. According to thisembodiment, no leads 38a, 38b are employed, but only piezoelectricceramics members 34a , 34b and a shim 32 are gripped between first andsecond fixing plates 6a, 6b. More specifically, electrodes 36a, 36b areshorter than the piezoelectric ceramics members 34a , 34b on the shim32, and lead wires for applying a voltage to the electrostrictive deviceare connected to one corner of the electrodes 36a, 36b near the fixingplates 6a, 6b which grip the piezoelectric ceramics members 34a , 34b.

Since the electrodes 36a, 36b are not gripped by the fixing plates 6a,6b and the piezoelectric ceramics members 34a , 34b are gripped by thefixing plates 6a, 6b, the electrostrictive device retains its ownrequired rigidity while reducing creeping.

Even if there were leads 38a, 38b, any problem resulting from creepingcould be avoided by not gripping such leads 38a, 38b with the fixingplates 6a, 6b. Other embodiments from such a standpoint will bedescribed with reference to FIGS. 17 through 19.

According to an embodiment shown in FIG. 17, first

fixing plates 6a, 6b have slots 40a, 40b defined and second fixingplates 6a, 6b have slots 40a, 40b defined respectively in theirconfronting surfaces. The slots 40a, 40b have a depth and length whichare the same as the thickness and length of the leads 38a, 38b extendingon the piezoelectric ceramics members 34a , 34b. Even when the end ofthe electrostrictive device 30 is gripped by the fixing plates 6a, 6b,the leads 38a, 38b are not gripped by the fixing plates 6a, 6b but aresnugly received in the slots 40a, 40b, respectively, so that theelectrostrictive device 30 is free of creeping.

In an embodiment illustrated in FIGS. 18 and 19, leads 38a, 38b aredisposed respectively in slots 42a, 42b defined respectively inpiezoelectric ceramics members 34a , 34b so that the leads 38a, 38b donot project from the surfaces of the piezoelectric ceramics members 34a, 34b . Therefore, even if the electrostrictive device is gripped byfixing plates 6a, 6b, the leads 38a, 38b are not gripped by the fixingplates 6a, 6b, thereby making the electrostrictive device free ofcreeping.

FIG. 20 shows a further embodiment in which two pairs of spacers 44a,44b are attached to the outer exposed surfaces, respectively, of thepiezoelectric ceramics members 34a , 34b in complementary relation tothe thickness and length of the leads 38a, 38b. The spacers 44a, 44b mayalternatively be fixed to the fixing plates 6a, 6b, respectively. Theelectrostrictive device of this embodiment can avoid creeping as thefixing plates 6a, 6b are not directly pressed against the leads 38a,38b.

In each of the above embodiments, the piezoelectric ceramics members 34a, 34b of the electrostrictive device 30 are gripped by the fixing plates6a, 6b to give a desired degree of rigidity to the electrostrictivedevice 30.

However, the piezoelectric ceramics members 34a , 34b may not be grippedif the desired rigidity can be kept by another means. FIG. 21 shows anembodiment based on such a concept.

In the embodiment of FIG. 21, a T-shaped holder 46 of a relatively largethickness is provided which is to be fixed to a base by screws (notshown), and a piezoelectric ceramics member 34a is fixed to the holder46 by soldering or adhesive bonding. As illustrated, electrodes 36a, 36bterminate short of the soldered or bonded region on the holder 46. Withthe piezoelectric ceramics members 34a, 34b attached to the holder 46,the electrostrictive device can easily be installed in position, and canalso easily be adjusted in position.

Further embodiments of the present invention are shown in FIGS. 22 and23. In the embodiment of FIG. 22, an electrostrictive device 30 includesa T-shaped shim 32 having a region 48 with spaced holes 50 definedtherein for the passage of fastening screws. The shim 32 has anotherregion 52 which is sandwiched between piezoelectric ceramics members34a, 34b applied respectively to lower and upper surfaces thereof withinsulating members therebetween. Electrodes 36a, 36b are appliedrespectively to the piezoelectric ceramics members 34a, 34b. Thepiezoelectric ceramics members 34a, 34b and the electrodes 36a, 36b donot cover the region 48 where the holes 50 are defined.

A nozzle flapper mechanism incorporating the electrostrictive device 30shown in FIG. 22 is constructed as follows:

The shim 32 is placed on the first fixing plate 6a, and the secondfixing plate 6b is placed on the shim 32 over the holes 50. Thefastening screws 10 are threaded through the holes defined in the secondfixing plate 6b and the holes 50 to secure the electrostrictive device30. Since the electrodes 36a, 36b and the piezoelectric ceramics members34a, 34b do not extend into the region 48 which is tightened by thefastening screws 10, only the shim 32 is subjected to tightening forcesby the fastening screws 10. Accordingly, no adjustments are requiredwith respect to such tightening forces when fixing the electrostrictivedevice 30 between the first and second fixing plates 6a, 6b. Thepiezoelectric ceramics members 34a, 34b are fixed to the shim 32 throughthe intermediary of the insulating layers without any adhesive.Therefore, any voltage applied to the electrostrictive device is notadversely affected by an adhesive.

When a voltage is applied to the electrostrictive device 30 to convertan electric signal to a pneumatic pressure signal, the electrostrictivedevice 30 can operate stably without any concern over tightening forcesapplied thereto. The electrostrictive device 30 can effect accuratecontrol especially when it is to be driven by a low voltage.

FIG. 23 shows an embodiment in which a shim 32 has a simpler rectangularshape. The shim 32 has a region where electrodes 36a, 36b andpiezoelectric ceramics members 34a, 34b are not applied. Such a regionis gripped by the first and second fixing plates 6a, 6b to make theelectrostrictive device free of creeping.

While a nozzle flapper mechanism is composed of a single bimorphelectrostrictive device in each of the previous embodiments, the presentinvention is also applicable to a laminated electrostrictive deviceassembly comprising a plurality of electrostrictive devices as shown inFIGS. 24 and 25.

In the embodiment of FIGS. 24 and 25, the laminated electrostrictivedevice assembly includes a plurality of piezoelectric ceramics members70a through 70d, and electrodes 72a through 72e attached to faces andbacks of the piezoelectric ceramics members 70a through 70d. Thelaminated electrostrictive device assembly includes no shim, but has thesame electrode structure as that of the electrodes 36a, 36b as shown inFIG. 14. The electrodes 72a, 72c, 72e have leads which are disposed inone localized position, and the electrodes 72b, 72d have leads which arelocated in another localized position which is on an opposite side tosaid one localized position. The leads are positioned in this manner inorder to prevent themselves from being localized in one position in thestacked construction of the piezoelectric ceramics members.

The electrodes 72a, 72c, 72e are electrically connected to each other bya single electric conductor 74, whereas the electrodes 72b, 72d areelectrically connected to each other by a single electric conductor 76.

FIGS. 26 through 28 shows still another embodiment which issubstantially similar to the embodiment of FIGS. 24 and 25, except forthe shape of electrodes applied to piezoelectric ceramics members 80athrough 80d. The electrodes shown in FIGS. 26 through 28 are rather of astructure which is substantially the same as the electrode structureshown in FIG. 15. However, in this embodiment, the electrodes 82a, 82c,82e are electrically connected to each other by an electric conductor84, whereas the electrodes 82b, 82d are electrically connected to eachother by an electric conductor 86. With the illustrated laminatedstructure, the electrostrictive device assembly can be flexed to alarger extent, and the piezoelectric ceramics members can retain adesired degree of rigidity without the need for a shim.

It is possible to employ twenty through forty electrostrictive devicesin the laminated assembly shown in FIGS. 24 through 28.

With the present invention, as described above, the electrodes of theelectrostrictive device are not gripped by the fixing plates, and theregion in which the piezoelectric ceramics members are subjected toexpansion and contraction upon application of a voltage to theelectrodes is free from tightening forces produced by the fixing plates.Therefore, the electrostrictive device and hence the nozzle flappermechanism incorporating the same are not adversely affected by suchtightening forces, and hence undergo as small creeping as possible. Thenozzle flapper mechanism is thus capable of accurately controlling itsnozzle back pressure.

Although certain preferred embodiments have been shown and described, itshould be understood that many changes and modifications may be madetherein without departing from the scope of the appended claims.

What is claimed:
 1. A nozzle flapper mechanism comprising:anelectrostrictive device; a plate member coupled to said electrostrictivedevice; a nozzle having an orifice facing the plate member on saidelectrostrictive device; and means for applying a voltage to saidelectrostrictive device to keep a nozzle back pressure constant or varythe nozzle back pressure; said electrostrictive device comprising aplurality of piezoelectric ceramics members, and a plurality ofthin-film electrodes disposed on faces and backs of said piezoelectricceramics members; wherein said electrodes have leads extendingrespectively therefrom, said leads also being disposed on the faces andbacks of said piezoelectric ceramics members positioned to one sidethereof, the lead from each of said electrodes being positioned on anopposite side of the electrostrictive device with respect to the leadfrom an adjacent one of said electrodes.
 2. A nozzle flapper mechanismaccording to claim 1, further including an electric conductor connectedto alternating ones of said electrodes on said piezoelectric ceramicsmembers and connecting said alternating ones of the electrodes to apower supply.
 3. A nozzle flapper mechanism according to claim 1,wherein the leads from said electrodes are positioned alternately onopposite sides.